Package for compounding rubber and compounded rubber

ABSTRACT

A package comprised of (A) an article selected from unvulcanized rubber or compounding ingredients therefor and (B) a protective film of a thermoplastic ethylene/vinyl acetate copolymer containing anti-block agent and having a vinyl acetate content in the range of 11 to 22 percent. The invention further relates to a compounded rubber comprised of a mixture of unsaturated rubber and a package of compounding ingredients contained in the ethylene/vinyl acetate copolymer film.

TECHNICAL FIELD

This invention relates to packaged materials for compounding rubber andto rubber compounds therewith.

BACKGROUND ART

Unvulcanized rubber and compounding ingredients therefor are oftenpackaged by wrapping with thermoplastic film or placing in bags thereof.Polyethylene is conventially used because of its plasticity, antiblockproperty, because it can be obtained in a desirable melting temperaturerange and at a relatively low cost.

However, polyethylene is disadvantageous because, when mixed withunvulcanized rubber, does not disperse sufficiently in the matrix. Thisleaves minute areas within the matrix of the rubber when cured, whichare themselves not cured and are subject to degradation.

Various solutions have been proposed. Very low softening pointpolyethylene has been used. Compounded elastomericstyrene/butadiene/styrene block copolymer films have been used withsuccess but are considerably more costly than polyethylene and sometimesdo not provide an effective packaged article when its contents includeoil of the rubber-processing type. Although it has not been fullyascertained, it appears that films of ethylene/vinyl acetate copolymerscontaining about 28-30% vinyl acetate have been used although theinventors' evaluation of such films has indicated them to be generallyunsatisfactory and without sufficient strength under test to package andcontain rubber compounding ingredients, particularly when containing arubber processing oil.

Therefore, it is an object of this invention to provide packagedmaterials for compounding rubber with a suitable film and to providerubber compounded with such a package.

DISCLOSURE AND PRACTICE OF INVENTION

In accordance with this invention a package is provided which comprises(A) an article selected from at least one of unvulcanized rubber orcompounding ingredients for unvulcanized rubber packaged in (B) aprotective film having a thickness in the range of about 0.5 to about10, preferably about 1 to about 5, mils of a thermoplasticethylene/vinyl acetate copolymer containing an anti-block agent andhaving a vinyl acetate content in the range of about 11 to about 22,preferably about 14 to about 19, percent and further characterized, thatwhen having a thickness of about 2 to 4 mils, by a melting point in therange of about 85° C. to about 95° C., a minimum ultimate tensilestrength at 25° C. of about 1850 psi, an oil solubility melt index ofabout 63° C. to about 75° C. and a minimum of 300 percent modulus at 25°C. of about 700 psi.

It is understood that the film composite of this invention desirably cancontain various typical lubricants, fillers, pigments and dyes andstabilizers and is required to contain a minimal amount of anti-blockagent sufficient to provide an anti-block quality to the surface of thefilm.

Thus, in the practice of this invention, a method of compounding rubberis provided and the resulting compounded rubber, which comprises mixingunvulcanized rubber, particularly high unsaturation rubber, with thepackage of this invention containing conventional rubber compoundingingredients optionally followed by sulfur curing said prepared mixtureof rubber, packaging film and packaged ingredients. The invention isparticularly applicable where the compounding ingredients contain about0.5 to about 10 weight percent rubber processing oil.

In the further practice of this invention a packaged unvulcanizedrubber, particularly a high unsaturation rubber and particularly apackaged unvulcanized rubber for storage, comprises such unvulcanizedrubber substantially encompassed with a wrap of the film required forthis invention. In practice, the film is generally applied around theunvulcanized rubber, especially when in bale form, usually under sometension so that it more firmly wraps the rubber and then heat sealedagainst itself to complete the package.

The thermoplastic packaging film of this invention, containing aconventional-type anti-block agent, is characterized by being able to bepulled apart from itself after two sides being pressed together, withoutappreciably destroying the film itself.

In the practice of this invention, the film of the ethylene/vinylacetate copolymer can be formed by extrusion or solution cast methods.Extrusion is often preferred. For solution casting, the copolymer andanti-block agent may be dissolved in an organic solvent followed bymixing therewith any additionally required materials. The mixture may becast as a film onto a substrate, dried by evaporating the organicsolvent to yield the required composition in the form of a film and thefilm stripped from the casting substrate. Typically, the mixture canprobably be dried at a temperature of about 40° C. to about 150° C.depending primarily upon the organic solvent used. It should be readilyunderstood that if the composition is to be dried as a thin film,reduced temperatures and times can probably be used such as, forexample, a temperature in the range of about 70° C. to about 90° C. fora period of about 15 to about 60 minutes.

Various rubber compounding resins and ingredients especially resins suchas hydrocarbon resins can be packaged according to this invention andthen compounded with unvulcanized rubber. Representative of the variouscompounding ingredients are fillers, such as clay, silicates, calciumcarbonate and the like; accelerators, such as, for example, cadmiumdiethyldithiocarbamate, tetramethylthiuram disulfide, benzothiazyldisulfide and the like; antioxidants, such as the well-known substitutedthioesters and amine type; antiozonants, such as aniline derivatives,diamines and thioureas; curatives such as sulfur, sulfur providingcompounds and peroxides; ultraviolet agent such as substitutedbenzotriazoles and substituted benzophenones; color pigments, such asiron oxide, titanium dioxides and organic dyes; reinforcing pigments,such as carbon black, zine oxide and hydrated silicon compounds; andprocessing aids, such as silicon dioxide, pumice, stearate and rubberprocessing oils.

In this manner, the term "packaged" relates to both bagged or wrappedcompounding ingredients, and particularly to mixtures thereof containingabout 0.5 to about 10 preferably about 0.5 to about 6, weight percentrubber processing oil. Such compounding ingredients, even whencontaining the rubber processing oil, are preferably free flowingwithout any substantial sticking together to impede their flow.

Unvulcanized rubber can also be advantageously packaged according tothis invention, usually as bales of rubber.

Representative of the various unvulcanized rubbers which can be packagedor which can be mixed with packaged compounding ingredients therefor arenatural rubber, synthetic cis-1,4-polyisoprene, polybutadiene, rubberybutadiene/styrene copolymers and rubbery butadiene/acrylonitrilecopolymers. All of such rubbers are of the high unsaturation type.Namely, they contain an appreciable amount of carbon-to-carbon doublebonds therein. Although this invention is partly directed to thepackaging of the high unsaturation-type rubbers, or compoundingingredients therefor, the low unsaturation type can also be used ifdesired. Representative of such low unsaturation rubbers are butylrubber, which is typically a copolymer containing a major amount ofisobutylene and a minor amount of isoprene, as well as the variousethylene/propylene copolymers and rubbery terpolymers ofethylene/propylene and a minor amount of non-conjugated diene.

An anti-block additive for the film of the package is particularlyuseful where the packaged material is rubber which is to be stacked or"containerized" together in order to prevent them from sticking to eachother and making them virtually impossible to separate without actuallydestroying portions of the package and material. The importance of suchan advantage is amplified by the following discussion.

Polyethylene film (PE) is generally used to overwrap bales of rubber orto package compounding ingredients therefor to simplify handling anduse. For most applications, the overwrapped bale is used intact; thus,the bale is charged into a banbury or another suitable mixer and the PEfilm is mixed into the rubber compound during the mixing cycle. However,in various applications, the polyethylene film has not been sufficientlydispersed and has caused defects to occur in the end-product curing useand is, therefore, not a suitable overwrap or packaging material orcontainer bag.

Films of this invention disperse substantially readily in a rubbercompound when mixed using conventional equipment. Even if completedispersion is not achieved, defects in the rubber, when cured, from thefilm are minimized because of its solubility and/or dispersability andplacticity in the rubber matrix.

For further understanding of this invention, reference may be had to theaccompanying drawing in which

FIG. 1 depicts a package comprised of rubber packaged in the requiredethylene/vinyl acetate copolymer film compounding ingredients and

FIG. 2 shows a package of an unvulcanized rubber with the film.

Referring to the drawings, FIG. 1 shows a package comprised of a bag ofethylene/vinyl acetate film 2 containing about 16 percent vinyl acetateand having an opening at its top 3 which can be optionally sealed 4,such as by heat sealing. The package 1 contains a mixture ofconventional compounding ingredients 5 for unvulcanized, highunsaturation rubber which contains about 5 weight percent rubberprocessing oil mixed therewith.

FIG. 2 shows a packaged bale 6 of high unsaturated rubber 7, optionallycompounded by mixing about 3.5 parts by weight of the package 1 of FIG.1 with 40 parts by weight natural rubber and 60 parts by weightpolybutadiene rubber, packaged with the required film for this inventionand heat sealed 8.

The practice of this invention is further illustrated by reference tothe following examples which is intended to be representative ratherthan restrictive of the scope of the invention. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1

A series of films having a thickness in the range of about 2 to 4 milswere obtained. The individual tough translucent films had various vinylacetate derived contents ranging from 5 to 29 percent.

A silica anti-block agent was included in the composition of the films.

The various ethylene/vinyl acetate copolymer films evaluated are shownin the following Table 1 and identified herein as films or Examples A-G.Example G was actually a physical blend of polyethylene and poly(vinlyacetate) rather than a copolymer.

                  TABLE 1                                                         ______________________________________                                        Films    Percent Vinyl Acetate                                                                          Softening Point.sup.1                               ______________________________________                                        A         5                  225° F.                                   B        12               208                                                 C        15               191                                                 D        18               189                                                 E        20               189                                                 F        29               126                                                 G        28               N/A.sup.2                                           ______________________________________                                         .sup.1 determined by differential scanning calorimeter(DSC)                   .sup.2 not applicable since the film was a physical mixture              

The films were first evaluated or tested for (1) dispersability inunvulcanized rubbers which were then sulfur vulcanized and examined. Ifthe film passed this test, it was submitted to a stacking test (2) whichcomprised filling bags made from films with 20 pounds of rubbercompounding ingredients containing about 0.5 to about 6 weight of arelatively high aromatic-type rubber processing oil and stacking thepackages to an extent of five packages high in a heated, or hostile,environment of about 100° F. for a period of about six days; and (3) ahandling test which comprised actual use under factory conditions.

Thus, generally, if the film did not pass the dispersability test, itwas not submitted to the further tests.

The results of the tests are shown in the following Table 2 with thefilms or experiments, A-G corresponding to the films A-G of Table 1.

                  TABLE 2                                                         ______________________________________                                                Dispersion  Stacking    Handling                                      Film    Test No. 1  Test No. 2  Test No. 3                                    ______________________________________                                        A       failed      N/A         N/A                                           B       passed      passed      passed                                        C       passed      passed      passed                                        D       passed      passed      passed                                        E       passed      passed      passed                                        F       passed      passed      failed                                        G       failed      N/A         N/A                                           ______________________________________                                    

Results of these tests show that (1) ethylene/vinyl acetate copolymerfilms containing from 12 to 20% vinyl acetate content passed testsdesigned to determine their suitability for use as packaging films forrubber compounding ingredients which are to be mixed and cured withsulfur vulcanizable rubber; (2) copolymers with substantially more than20% or less than 12% vinyl acetate content were found to not entirelypass these tests; and (3) physical blends of polyethylene and asubstantial amount of poly vinyl acetate did not pass the dispersiontest although a copolymer with similar vinyl acetate content did.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

We claim:
 1. A package which comprises (A) an article selected from atleast one of unvulcanized rubber or compounding ingredients forunvulcanized rubber packaged in (B) a protective film having a thicknessin the range of about 0.5 to about 10 mils of a thermoplasticethylene/vinyl acetate copolymer containing an anti-block agent andhaving a vinyl acetate content in the range of about 11 to about 22percent and further characterized, when having a thickness of about 2 to4 mils, by a melting point in the range of about 85° C. to about 95° C.,a minimum ultimate tensile strength at 25° C. of about 1850 psi, an oilsolubility melt index of about 63° C. to about 75° C. and a minimum 300percent modulus at 25° C. of about 700 psi.
 2. The package of claim 1where said packaged article is at least one compounding ingredient forunvulcanized rubber and where its said protective packaging film has athickness in the range of about 1 to about 5 mils where said copolymerhas a vinyl acetate derived content in the range of about 14 to about 19percent.
 3. The package of claim 1 where said article is an unvulcanizedhigh unsaturation rubber.
 4. The package of claim 2 where saidcompounding ingredients are free flowing and are selected from at leastone of clay, silicates, calcium carbonate, cadmiumdiethyldithiocarbamate, tetramethylthiuram disulfide, benzothiazyldisulfide, substituted thio esters and amine type antioxidants, anilineantiozonant derivatives, diamines and/or thiourea curatives selectedfrom sulfur, sulfur providing compounds and peroxides, ultravioletagents selected from substituted benzotriazoles and substitutedbenzophenones; color pigments, selected from iron oxide, titaniumdioxides and organic dyes; reinforcing pigments selected from carbonblack, zinc oxide and hydrated silicon compounds; silicon dioxide, andalso a minor amount of rubber processing oil when mixed with at leastone other of such compounding ingredients.
 5. A compounded rubbercomprised of a mixture of unsaturated rubber and the package of claim 1.6. A compounded high unsaturation rubber with the package of claim 2,where said compounding ingredients are relatively free flowing andcontain about 0.5 to about 10 weight percent rubber processing oil. 7.The compounded rubber of claim 6 where said compounding ingredients arefree flowing and are selected from at least one of clay, silicates,calcium carbonate, cadmium diethyldithiocarbamate, tetramethylthiuramdisulfide, benzothiazyl disulfide, substituted thio esters and aminetype antioxidants, aniline antiozonant derivatives, diamines and/orthiourea, curatives selected from sulfur, sulfur providing compounds andperoxides, ultraviolet agents selected from substituted benzotriazolesand substituted benzophenones; color pigments, selected from iron oxide,titanium dioxides and organic dyes; reinforcing pigments selected fromcarbon black, zinc oxide and hydrated silicon compounds; silicondioxide, and also a minor amount of rubber processing oil when mixedwith at least one other of such compounding ingredients.
 8. Thecompounded rubber of claim 2 or 3 where said high unsaturation rubber isselected from at least one of natural rubber, syntheticcis-1,4-polyisoprene, polybutadiene rubbery copolymers of1,3-butadiene/styrene and/or rubber copolymers of butadiene andacrylonitrile.
 9. A packaged, high unsaturation unvulcanized rubberwhich comprises such unvulcanized rubber substantially encompassed witha wrap of a protective film having a thickness in the range of about 0.5to about 10 mils of a thermoplastic ethylene/vinyl acetate copolymercontaining an anti-block agent and having a vinyl acetate content in therange of about 11 to about 22 percent and further characterized, whenhaving a thickness of about 2 to 4 mils, by a melting point in the rangeof about 85° C. to about 95° C., a minimum ultimate tensile strength at25° C. of about 1850 psi, an oil solubility melt index of about 63° C.to about 75° C. and a minimum 300 percent modulus at 25° C. of about 700psi.
 10. A method of compounding rubber which comprises mixingunvulcanized rubber with the package of claim
 1. 11. The method of claim10 where said rubber is a high unsaturation rubber where said copolymerof said film has a vinyl acetate derived content in the range of about14 to about 19 percent.
 12. The sulfur cured compounded rubber of claim5.
 13. The sulfur cured compounded rubber of claim
 6. 14. The sulfurcured compounded rubber of claim 7.